5.2 Igneous Rocks

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Vocabulary

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Extrusive Rocks: igneous rock formed from lava that erupted onto earth's surface
Intrusive Rocks: igneous rock formed when magma hardened beneath earth's surface
Porphyritic Texture:large crystals are scattered on a background of much smaller crystals

Outline

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• Characteristics of igneous rocks
  • classified according to:
    • origin
    • texture
    • mineral composition
  • origin
    • extrusive rock
      • formed by lava that erupted onto earth's surface
      • basalt is most common
    • intrusive rock
      • formed when magma hardened beneath earth's surface
      • granite is most common
  • texture
    • can be:
      • fine grained
      • coarse grained
      • glassy
      • porphyritic
    • fast cooling lava forms fine grained igneous rocks with small crystals
    • slow cooling magma forms coarse grained rocks with large crystals
    • intrusive and extrusive rocks usually have different textures
    • intrusive rocks have larger crystals than extrusive rocks
  • mineral composition
• Uses of igneous rocks
  • tools and building materials
  • basalt is crushed to make graval

Diagram

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